1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device having a power circuit such as a power source voltage generating circuit which includes power transistors and power ICs (which are hereinafter referred to as "power elements") and a control circuit which is provided for the power circuit and includes integrated circuit elements having no power elements and a method of manufacturing the same.
2. Description of the Related Art
A conventional semiconductor device, particularly, a module product has a circuit pattern formed on a single circuit board and a plurality of pellets including ICs, LSIs or the like mounted on the circuit board. The electrical connection between the pellets can be made by electrically connecting the electrodes and circuit patterns of the respective pellets to each other. After this, the circuit board is resin-sealed together with the pellets. At present, the technique of mounting the semiconductor device at a high density is rapidly developed. Relatively severe conditions which permit a large number of pellets to be mounted on the smallest possible package and permit power elements and integrated circuit elements (which are hereinafter referred to as "control elements") used in the control circuit as the mounting semiconductor elements are required to the package. Further, it is required to use a power element having a large power consumption and mount a plurality of power circuits in a single package. Consequently, it becomes strongly required to enhance the heat radiation efficiency.
The above conventional module product is explained with reference to FIG. 1. Semiconductor elements (pellets) 5 and 9 are mounted on a circuit board 4. The pellets are electrically connected to a circuit pattern formed on the circuit board 4 via respective bonding wires 6. The pellet 5 includes a power element and tends to generate a large amount of heat. The pellet 5 is thus referred to as a "power pellet" in the following description. The pellet 9 corresponds to a control circuit including normal control elements. Signals from the power pellet 5 are, for example, supplied to an external lead 2 connected to the other pellet 9 and external circuit through the bonding wire 6 and the circuit pattern of the circuit board 4. The circuit board 4 is fixed on a heat radiating device (heat sink) 3 for radiating heat generated from the pellet to the exterior. The heat sink 3 having the circuit board 4 is coated with and protected by a cove 1 formed of plastic resin or the like. Since the semiconductor device is generally formed of a single circuit board, it is impossible to sufficiently cope with the high-density mounting.
Under the severe conditions of the reduced package size and the enhanced mounting density, there is a limitation on the number of pellets which can be mounted on the single board. Further, since a single board is used, it is difficult to mount the control element together with the power element unless a particular structure which may be obtained by attaching a heat spreader, for example, is provided. In order to enhance the mounting density, it can be easily considered to stack a plurality of boards having elements mounted thereon and this is possible in the normal printed circuit. However, in the semiconductor device which includes a power element and tends to generate heat, heat radiation devices must be attached to the respective circuit boards. As a result, it is difficult to realize such a structure and therefore the above idea is not realized until now.